382 THE HUMAN SPECIES 



associated with complete or partial absence of teeth, are the 

 hairless dogs with incomplete dentition, especially the incisors, 

 the canines and pre-molars. 



The most interesting cases of deformity owing to imperfect 

 development are those in which an acquired deformity is 

 transmitted, a possibility which is still very irrationally dis- 

 puted. Darwin relates, as absolutely credible, the case of a 

 child with a shortening of the little finger of the right hand 

 whose father had lost the same finger ; also the case of a man 

 whose eye had been removed owing to suppurative disease, 

 and whose child had micro-ophthalmos on the same side of the 

 head. Acquired defects are also transmitted in animals, such 

 as dogs, cats, horses, cows. It is not known with certainty 



whether all tailless cats and dogs 

 are descended from ancestors who 

 once lost their tails by mechanical 

 violence. The fact of its occasional 

 occurrence cannot, however, be 

 denied. A stag which had lost 

 one antler produced one-antlered 

 progeny, and a cow, one of whose 

 horns had been lost owing to sup- 

 puration, afterwards brought three 

 one-horned calves into the world. 

 (/?) The deformities caused by 



FIG. 194. Hare-lip. (Bardeleben.) 



arrested development are either 



due to the persistence of an earlier embryonic condition till 

 birth, or to an error in the original development of the part. 

 They are common to animals (domestic) and ' man. They 

 result in fissures (Fig. 194), or in the closure of cavities and 

 canals which are normally open, in the union of normally 

 separate parts, and in the stunting and deficiency of certain 

 organs. 



In this class may be included the complete or partial union 

 of the small bones of the extremities which normally are 

 separate. In man" the congenital union of two or more fingers 

 in one or both hands may occur in varying degrees. It may 

 be merely a kind of partial webbing, or may be a complete 

 union of the skin of two fingers right up to the knuckles. Web- 



